Ammonia-based fertilizers have long been utilized as means for augmenting the nitrogen availability within the nitrogen cycle. Deleteriously, however, bacterial oxidation of the ammonia therein converts it initially to nitrite and then to nitrate before it can be utilized by the plants. As is well known in the art, nitrites are toxic. The nitrates are usually lost as a nitrogen source by leaching out and ultimate reduction to nitrogen.
In order to eliminate such nitrification processes, urea has long been used as a slow, or sustained, nitrogen-release source. However, the enzyme urease is present in the soil. Urease is functional to convert urea to ammonia extremely rapidly.
Similarly, urea has been utilized as an ammonium source for ruminants. But, urease is also present in the rumen of such animals. Rapid release of ammonia within the rumen will cause the animal undue distress, and therefore is not desirable.
In order to circumvent the problems associated with urea the prior art processes have provided various condensation products of the reaction between urea and formaldehyde (hereinafter referred to as the ureaformaldehyde reaction).
The reaction of urea with formaldehyde and the resultant products are well documented.
The reaction products will vary depending upon the reaction conditions. Under basic conditions the yield of methylol compounds predominates. Under acidic conditions, methylene-bonded compounds are produced.
U.S. Pat. No. 3,759,687, issued to A. Nobell, and U.S. Pat. No. 2,644,806, issued to M. A. Kise, exemplify the prior art teachings on the urea-formaldehyde reaction undertaken in aqueous solution and the properties of the condensation products thereof.
It will be readily appreciated that such condensation products comprise urea-formaldehyde polymers having high molecular weights. The control of the degree of polymerization however, is difficult using these prior art processes. Typically, the polymer chains may comprise from 4 to 7 urea units. It is undesirable to have such high molecular weight polymers because bacteria have difficulty in breaking down polymer chains which contain more than 4 or 5 urea units therein. Additionally, such compositions exhibit solubility only in hot water. Therefore, when these prior art compositions are utilized as, for example, fertilizers, in order to be effective they must be ploughed into the ground.
There exists, therefore the need for a sustained nitrogen-release urea-formaldehyde product possessing the following characteristics:
low molecular weight polymer chains preferably containing no more than four urea units; and PA0 cold water solubility whereby the need for ploughing the product in would be eliminated as the product would go into solution readily in rain water or the like; PA0 simplicity; PA0 inexpensiveness; and PA0 imparting a degree of controllability to the polymerization process.
and for a process characterized by the following: